A number of different wireless communication techniques have been developed, including frequency division multiple access (FDMA), time division multiple access (TDMA) and various spread spectrum techniques. One common spread spectrum technique used in wireless communication is code division multiple access (CDMA) signal modulation in which multiple communications are simultaneously transmitted over a spread spectrum radio-frequency (RF) signal. Some example wireless devices that have incorporated CDMA technology include mobile phones such as cellular and satellite radiotelephones, PCMCIA cards incorporated within portable computers, personal digital assistants (PDAs) equipped with wireless communication capabilities, and the like.
Wireless networking techniques have also been developed in order to allow wireless devices to share information and resources via wireless communication. Examples of wireless devices used in wireless networks include laptop or desktop computers, personal digital assistants (PDAs), mobile phones, data terminals, data collection devices, household appliances, and other portable and non-portable wireless computing devices.
One family of standards developed to facilitate wireless networking is set forth in the IEEE 802.11 standard. The original IEEE 802.11 standard provides wireless data transfer rates of 1-2 Megabits per second (Mbps) in a 2.4-2.483 Gigahertz (GHz) frequency band (hereafter the 2.4 GHz band). However, a number of extensions to the original IEEE 802.11 standard have been developed in an effort to increase wireless data transfer rates.
The IEEE 802.11b standard (sometimes referred to as 802.11 wireless fidelity or 802.11 Wi-Fi) provides 11 Mbps transmission, with a fallback to 5.5, 2.0 and 1.0 Mbps in the 2.4 GHz band. The IEEE 802.11g standard is another extension of the IEEE 802.11 standard. The IEEE 802.11g standard utilizes orthogonal frequency division multiplexing (OFDM) in the 2.4 GHz frequency band to provide data transmission at rates up to 54 Mbps. The IEEE 802.11g standard also provides backwards capability with 802.11b networks. The IEEE 802.11a standard is an extension of IEEE 802.11 standard that utilizes OFDM in a 5 GHz frequency band to provide data transmission at rates up to 54 Mbps. Other wireless networking protocols include “Bluetooth protocols” developed by the Bluetooth Special Interest Group. Additional extensions to the IEEE 802.11 standard, as well as other wireless local area network (WLAN) standards will likely emerge in the future.
Wireless receivers typically make gain adjustments to the received signal via analog closed-loop automatic gain control (AGC). Then, once the received signal has been scaled, the scaled signal can be examined or measured in order to determine whether the signal corresponds to an information signal supported by the system. If so, demodulation of the wireless signal can be performed.
More recently, discrete gain states have been implemented in wireless devices in lieu of, or in addition to analog AGC. When discrete gain states are used, the wireless device scales a received signal by selecting one of a plurality of discrete gain states. Typically, the wireless device selects the gain state based on an estimated signal strength of the received signal, i.e., an estimate of signal power at the antenna of the receiving device. If the estimated power of the received signal at the antenna is too low, the gain state can be selected to increase one or more gains used in signal conditioning. Alternatively, if the estimated power of the received signal at the antenna is too high, the gain state can be selected to decrease the gain(s). For example, after estimating the signal strength at the antenna, the estimated signal strength may be mapped to the most desirable gain state, which in turn maps to one or more gains applied at amplifiers, mixers, or other signal conditioning components.
The term “switchpoints” refer to the estimated signal strengths at which gain state switching occurs. Calibration of the switchpoints is conventionally performed, in which wireless devices are tested to define switchpoints that can be programmed into the wireless devices. Such calibration can be very costly and time consuming, increasing the manufacturing cost of wireless devices. Moreover, calibration to account for temperature effects and frequency offsets is often performed based on the measured characteristics of only a subset of the devices. These calibration concerns, as well as challenges in signal strength estimation, may cause inaccuracy in switchpoints, which in turn can affect performance of the wireless device.